1. Field of the Invention
The present invention is related generally to snub valves and, more particularly, to a snub valve that provides two alternative fluid flow paths between a source of motive fluid and a device which is moved by the use of hydraulic pressure.
2. Description of the Prior Art
Various types of valve configurations are known to those skilled in the art. Typically, a valve comprises a moving component which can be caused to move, either axially or rotatably, within another component for the purpose of alternatively permitting a fluid to flow through the valve or prohibiting such a flow.
U.S. Pat. No. 1,951,065, which issued to Ryd on Mar. 13, 1934, discloses a pneumatic rock drilling machine that is combined with a change-over valve which is adapted to automatically effect the reversal of the feeding device at a definite point in its movement. It is operated by the driving medium of the machine and may be adapted to throttle the supply of the driving medium to the striking mechanism during the returning movement of the machine.
U.S. Pat. No. 4,650,093, which issued to Gold et al on Aug. 14, 1984, discloses a hydraulic fuse valve that is operable to shut off fluid flow when a fluid conducting line down stream of the fuse has ruptured. The fuse is actuated by two forces which are generated by a pressure differential caused by sudden decompression of the fluid and developed across two variable, sharp edge, viscosity insensitive orifices that are positioned in series and separated by a flow cut-off and sealing surface. The fuse assembly includes a manually adjustable bypass arrangement and a pressure peak attenuating control.
U.S. Pat. No. 4,436,111, which issued to Gold et al, on Mar. 13, 1984, discloses a hydraulic fuse that is used for shutting off the line flow after the flow through the line reaches a certain maximum predetermined value. The spring biased movable closure element of the fuse is actuated by two force generating members positioned in series. The upstream member generates a high actuating force that rapidly increases with the displacement of the movable closure.
U.S. Pat. No. 4,343,328, which issued to Junger on Aug. 10, 1982, discloses a flow sensing check valve that comprises a velocity fuse mounted in the second of two ports. When the velocity fuse senses a preselected difference in flow, it causes a poppet valve to seat.
Copending patent application Ser. No. 46,472, filed on May 4, 1987 by Jones et al and assigned to the assignee of the present application, describes a bi-directional snub valve which performs a function which is similar to the function performed by the present invention. The bi-directional snub valve disclosed in the Jones et al application utilizes two check valves connected in parallel with opposite polarity in association with a piston for the purpose of decreasing fluid flow through a valve as a movable object approaches its end-of-travel position. The check valves cooperate with the piston to slow the movement of the movable object as it reaches its end position but permits the movable object to be moved away from its end of position at full speed.
As described above, many applications in which fluid flowing through an orifice is used as a fuse member to activate or deactivate an operation or component when a predetermined quantity of fluid flows through the orifice are known to those skilled in the art. This concept is generically referred to as a hydraulic fuse and is used to describe the use of an orifice to operate some mechanism after a predetermined quantity of fluid has passed through the orifice from one chamber to another.